Laptop battery life on FreeBSD

[Chuck Swiger]

On Jan 27, 2009, at 4:49 PM, Shawn Badger wrote:
>> Have you tried reducing HZ to 100 (put kern.hz="100" in /boot/ 
>> loader.conf and reboot)?
>> Are you running powerd?  Look into "sysctl hw.acpi" and "sysctl  
>> debug.cpufreq"....
>>
> Thanks for the ideas Chuck.  I lowered kern.hz to 100 as you  
> suggested (does this affect the kernel's ability to track time in  
> milliseconds?  ie. if I want to run a benchmark using the 'time'  
> utility?).

Changing the scheduler quantum won't affect the system clock or the  
ability to do millisecond-level timing of userland processes.  It does  
affect the granularity of things like ipfw/dummynet if polling is  
enabled, but shouldn't have any real negative effects otherwise.

For most of Unix history, HZ=100 was a common default, and the reduced  
context switch frequency should result in a decent improvement to  
power drain.  If you have a concern, consider comparing against HZ=250  
and see how the battery life and responsiveness or granularity of  
network traffic, etc feel....

> And the output of the two sysctl queries is posted here:   http://pastebin.com/m5ae8aa1c
>
> I'm not very familiar with acpi, so if you see anything that could  
> be optimized, I'd appreciate the feedback.

I have limited experience with running FreeBSD on a laptop personally  
[1], so others will likely have more relevant feedback; I'm just aware  
of some starting points.  :-)

Regards,
-- 
-Chuck

[1]: I've helped a few people run FreeBSD 5.x/6.x on various IBM  
ThinkPads (circa T.42s) an maybe an HP Pavillion or Dell Latitude, and  
I've run FreeBSD a bit on a Mac mini and a MacBookPro (2,2), but I  
don't use FreeBSD on a laptop regularly...I think of it as a server  
OS.  :-)